Method for processing plastic sheets



Patented Mar. 23, 1948 ...Marmor .Eon PRo srnnrl:

CESSSINGfPI-IASTIC Sheldon LfGordom lMadison, 3W-is., assigner, "by-imesne assignments, :.to the `EUnited States --Lfrmericar-asirepresented by the Secretary ofivar i ApplieationDeeniber10, 1945,.SerialfNo. 1,634,044

2 claims. (ciers-@2181 This invention relates tothe-rolling of plasticmaterials and, more particularly, to a method of rupturingil.bubbles*formed#duringrolling of hazardous plastic compositions.

In the manufacture'of-smokelessfpowder, vdiffr taining nitrocellulose-and gnitroglycerin. -ilhe y-rnixturemis `dumped onto 'horizontallydisposed Lheated differential--ro-llsas-a-wetepaste an, O lied tobringIabout-the -formation of -acolloided heet Von ithe-f faster roll.-During,-thisfhazardous :proces`s, protruding -bubblesofsteam" areformed 4-between the sheet and the faster roll as the moisture in thecharge is rapidly dissipated by the heated roll in combination with theheat generated by the rolling operation.

The formation of these bubbles presents a considerable re hazard in therolling of smokeless powder. 'I'he compression of the bubbles as theypass into the bite of the rolls causes them to burst and a firefrequently results. The theory has been advanced that escaping steamunder a relatively high pressure passing through a small break in thewall of a large bubble frictionally generates enough heat to causeignition of the charge.

Thus, the prevention of the compression of bubbles in the bite of therolls is a very desirable step in the diierential rolling of smokelesspowder as well as any other rolling operation where undesirable bubblesare likely to be formed.

An object of the present invention is to provide a method for rupturingprotruding bubbles attaining a predetermined height in plasticcomposition during rolling to prevent such bubbles from entering thebite of the rolls.

Other objects of the invention will appear hereinafter, the novelfeatures and combinations being set forth in the appended claims.

Generally described, the present invention comprises a method ofrupturing and deiiating protruding bubbles which are undesirably formedin a plastic sheet material and means for rupturing bubbles in saidplastic sheet material.

A preferred embodiment of the invention has been chosen for purposes ofillustration and description and is shown in the accompanying drawingforming a part of the specification, wherein reference symbols refer tolike parts wherever they occur.

Fig. 1 is a front elevational view of a preferred form of apparatus forthe embodiment of the invention.

Fig. 2 is a transverse sectional view of the ap- V`pamaztus illustrated"infFi'g, "lgjshowinfg ajplastic .Sheet beine formed h*on 'one "of' therolls of the apparatus.

,Figr' fis Ian .enlarged sectional` v iew 'of a portion 1'offtheapparatusitakenalong,line 3-.3 of `F'g. 1.

`With referenceto the 'drawing fa; conventional type diierential speedmill I0 with 'heated rolls -hasavliigjh speedrll-II 'ad'jacentto ailowvspeed ',rollF-,I-Z. f'Aibar'IiS'is rigidly supported at each'endfbyffframeemembersjof'the milll. The bar k-Il3 :is gsuperposed'infjuxtaposition 'to lfthe y high speed-rondt -The"bar"l3iis'providedwith sharp bubble rupturing projections or pins Ill at a predetermineddistance from and at suitable increments along the face of the highspeed roll II. The pins I4, as shown in Fig. 3, are preferably formed ofa shank I5 rigidly secured in the bar I3, a sharp point I6, and a sharpbarb I'I adjacent to the point I6.

As illustrated in Fig, 2, during rolling of a wet charge I8, such assmokeless powder, bubbles I9 are formed as the moisture is rapidly.

evaporated from the charge being worked on the heated high speed rollII. The charge I8 being formed into a plastic sheet is carried under thebar I3 in the direction indicated by arrow 2o and bubbles I9 protrudingabove the surface of said plastic sheet are ruptured by the pins ldbefore entering the bite of the rolls. The rupturing of the bubbles I9is greatly facilitated by the barbs I1 placed in a forward position asshown.

An example of the operation of the invention is given for the colloidingof a smokeless powder. The rolling mill utilized was of the typeillustrated in the drawing and had the following characteristicsConstant ro11 temperature 105 C.

Gap between the rolls.. .023 inch Peripheral speed of faster roll--Approx. 113 it.

per min.

Peripheral speed of slower roll-. Approx. ft.

per min.

Roll diameters 14 inches Roll lengths 30 inches The smokeless powdercomposition had the following formulation:

Parts by weight Nitrocellulose 49.50 Nitroglycerin 41.50 Ethylcentralite 9.00 Candelilla, wax 0.08

The above composition, properly mixed in water, blended, dewatered anddried to a moisture content o1 approximately 13% by weight, was placedon the rolls of the mill in charges of predetermined weights suitable tothe length of the rolls and size of sheet desired. The mill was providedwith bubble rupturing means as illustrated in the drawing. Protrudingbubbles, formed as the charge was worked on the faster roll, wereeciently and eiectively ruptured by the pins set two inches apart and0.4 inch above the faster roll.

In comparison with rolling operations not em- ,v

rembodiment of the invention, a plurality of knives, pins without barbs,circular cutters and the like similarly arranged over the plastic ma.-terial may be mentioned among alternating bubble rupturing means. y

It will be seen, therefore, that the advantages of the present inventionreside particularly in the processing of hazardous plastic material, butthat advantages also reside in any process where the bursting ofprotruding bubbles in a rolling 4 operation is required to improve theend product or the processing operation.

What I claim and desire to protect by Letters Patentis:

1. In the process of rolling an ignitable colloidable material, whereinprotruding bubbles are undesirably formed and present a potentialignition hazard if compressed between the rolls,

- the improvement which comprises rupturing and deflating the bubblesreaching a predetermined height before entry into the bite of the rolls.

2. In the process of diierential rolling smokeless powder whereinprotruding bubbles are undesirably formed and present a potentialignition hazard if compressed between the rolls, the improvement whichcomprises rupturing `and deating the bubbles reaching a predeterminedheight before entry into the bite of the rolls.

' SHELDON GORDON.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,184,016 Price May 23, 19162,055,002 Chandler Sept. 22, 1936 2,186,771 Smith Jan. 9, 1940 2,309,543Sawyer Jan. 26, 1943 2,383,694 Steiner Aug. 28, 1945 2,408,729 BrackettOct. 8, 1946

